1. Field of the Invention
The present invention relates to a communication apparatus that performs mass data transfer in a short range through an extremely low-power UWB communication scheme that uses a high-frequency wide band, and in particular to a communication apparatus that secures a horizontal communicable range in extremely low-power UWB communication that utilizes electric field coupling.
2. Description of the Related Art
Contactless communication is widely utilized as a medium for authentication information or value information on electronic money or the like. For example, NFC (Near Field Communication) developed by Sony Corporation and Royal Philips Electronics is an RFID standard defining the specifications of an NFC communication apparatus (reader/writer) that may communicate with each of a type-A IC card, a type-B IC card, and a FeliCa IC card complying with ISO/IEC 14443. NFC enables contactless bidirectional communication that uses a 13.56 MHz band and that is performed in proximity (within a range of 0 to 10 cm) through an electromagnetic induction scheme. Recently, contactless communication systems have been further applied to mass data transfer such as downloading and streaming of video and music data. Mass data transfer is preferably accomplished with a single user operation and completed in an access time that is perceptually as short as the time necessary for authentication and billing processes in the past. Therefore, a high communication rate is demanded.
A general RFID standard defines contactless bidirectional communication that uses a 13.56 MHz band and that is performed in proximity (within a range of 0 to 10 cm) on the basis of electromagnetic induction as a primary principle. The contactless bidirectional communication provides a communication rate of only about 106 kbps to 424 kbps. In contrast, TransferJet which uses an extremely low-power UWB (Ultra Wide Band) signal may be mentioned as a proximity wireless transfer technology applicable to high-speed communication (see Japanese Unexamined Patent Application Publication No. 2008-99236 and www.transferjet.org/en/index.html (as of Mar. 23, 2009), for example). The proximity wireless transfer technology (TransferJet) is basically a scheme for transferring a signal utilizing electric field coupling. A communication apparatus for TransferJet is formed of a communication circuit section that processes a high-frequency signal, a coupling electrode disposed away from a ground at a certain height, and a resonance section that efficiently supplies the high-frequency signal to the coupling electrode.
A compact reader/writer module for NFC communication suitable for embedded application has already been developed and manufactured, and is available for installation in various devices. Meanwhile, a cradle may be mentioned as an instrument that provides the above proximity wireless transfer function to existing information devices. For example, connecting a cradle incorporating a high-frequency coupler to the main body of a personal computer through a USB (Universal Serial Bus) enables data transmission and reception through proximity wireless transfer between the personal computer and a cellular phone or a digital camera incorporating the proximity wireless transfer function.
For example, a cradle device including a card reader/writer is proposed. When a camera-equipped portable device incorporating a contactless IC card is attached to the cradle device, the card reader/writer reads and writes image data through wireless communication with the contactless IC card (see Japanese Unexamined Patent Application Publication No. 2007-79845, for example). Further, a cradle that performs wireless communication, such as Bluetooth communication, with a digital camera is also proposed (see Japanese Unexamined Patent Application Publication No. 2007-28302, for example).
In the past, it was common to provide a cradle as a standard accessory or an optional accessory dedicated to each model. However, respective family members often own different models of products, and thus there tend to be a large number of cradles in home. Thus, in order to avoid that, it is considered to be preferable to introduce the concept of Universal Design and provide a cradle common to a plurality of models.
However, portable information devices such as cellular phones and digital cameras are varied in design and operability among models, and thus the shape of the main body of the devices and the installation position of the high-frequency coupler within the devices are not fixed. Therefore, even if a cellular phone is placed on a desktop (or on the floor) in the same posture and a cradle is placed adjacent to the cellular phone, the coupling electrode of the high-frequency coupler may not face the reading surface of the cradle appropriately.
For example, a cellular phone may be provided with a proximity wireless transfer function through the medium of a memory card. In this case, as shown in FIGS. 10A and 10B, the position of a memory card slot may be different among models. Thus, even if the main body of the cellular phone is placed in the same posture and approximated to the cradle, the same communication quality may not be obtained because the position of the high-frequency coupler may be different.
Proximity wireless transfer that utilizes extremely low-power UWB has a communication range of about 2 to 3 cm. The high-frequency coupler does not have polarization characteristics, and thus has a communicable range substantially in the shape of a hemispherical dome having substantially the same extension in the vertical direction and in the horizontal direction. On the other hand, assuming that the height and the thickness of the portable information device are respectively about 5 cm and 1 cm, the difference in height of the coupling electrode due to the difference in design among models or the difference in posture of the device placed on a desktop may be as large as about 5 cm. That is, variations in height of the coupling electrode according to the placement posture of the communication partner device may exceed the communication range supported by the proximity wireless transfer technology.